About 17% of the US population suffers from overactive bladder (OAB) and the associated economic cost is more than $26 billion per year. OAB is a poorly understood disorder characterized by increased urinary bladder smooth muscle (UBSM) contractility. In experimental animals, the large-conductance voltage-gated and Ca2+- activated K+ (BK) channel is a key regulator of UBSM membrane excitability and contractility. In general, inhibition of these ion channels leads to increased membrane excitability and contractility, whereas their activation hyperpolarizes the membrane and decreases contractility. However, the BK channel function and regulation in human UBSM is unknown. Our basic science research group, in collaboration with clinical scientists, is in a unique position to regularly utilize human UBSM tissues from donor patients to study BK channel function in humans and correlate the basic science findings with the clinical and urodynamic profile of the patients. Our long-term goal is to understand the mechanisms that regulate human UBSM BK channels under normal physiological conditions and to develop novel therapeutic strategies to control OAB. The objective of this application is to elucidate the physiological role and regulatory mechanisms of the BK channel in human UBSM contractility under normal physiological conditions. We will test the novel hypothesis that the BK channel determines the myogenic activity of human UBSM and it is regulated by cholinergic, 2- adrenergic, and differential Ca2+ signals with the following Aims: Aim 1. Elucidate the role of Ca2+ in the regulation of the BK channel in human UBSM myogenic activity; Aim 2. Elucidate the functional link between 2-adrenoceptors (2-ARs) and BK channels in UBSM; and Aim 3. Elucidate the functional link between muscarinic (M2 and M3) receptors and BK channels in UBSM. We will employ a combined approach, using state-of-the-art techniques, to determine the role of BK channels and their regulatory mechanisms in UBSM function from single molecules and isolated cells to intact tissue and the whole organism. Our team has the advantage of using full-thickness human UBSM tissues from open surgeries, which allows us to conduct advanced patch-clamp electrophysiology, functional studies on human UBSM contractility, and molecular biology experiments simultaneously. Thus, we can identify channel regulatory proteins, and then correlate BK channel activity with human UBSM contractility properties. Our research team's basic science and clinical expertise may lead to important translational observations. The proposed studies are expected to provide novel insights on BK channel function and regulation by cholinergic, 2-adrenergic, and Ca2+ signals in human UBSM. The results will have a significant impact on urological research with a strong potential to provide novel therapeutic approaches to help a large population of patients suffering from OAB.